The vast majority of individuals infected with trachoma are protected from the severe sequellae of the disease. Humans must have some type of immune response which protects over 90 percent of those infected. The objective of our research is to evoke that protective mechanism. We will attempt to isolate and identify the protective antigenic fraction(s) of chlamydial strains, particularly trachoma but also of other Group A isolates. Such studies are now feasible since large quantities of material are available through renografin gradient centrifugation. Protection/challenge experiments will be attempted in animals using isolated antigenic fragments. Current research has led to the finding that circulating antibody does not protect animals from local chlamydial infection. This research will be continued. Emphasis will be placed on identifying the respective contributions to protection by cell mediated immunity and of trachoma specific antibodies in eye secretions. We will seek to enhance the efficacy of topical vaccines in animal models by use of fractions of elementary bodies or matrix with improved immunogenicity. Adjuvants as well as agents which retain the antigens for longer periods in the conjunctivae will be used to increase the antibody or CMI responses. We will test in Saudi Arabia a revised strategy for antibiotic treatment of trachoma utilizing an immunological technique as an aid to greater efficiency in case finding in a program aimed at entire communities with holoendemic trachoma. Increased efficiencies of infectivity and growth of trachoma in cell culture suspensions will be sought. The immunological responses to sexually transmitted chlamydial disease in humans will be studied, utilizing specimens obtained from V.D. clinics as part of our study of gonorrhea. Diagnosis of chlamydial infections of the genital tract in humans by tests for the presence of specific antibodies will be attempted. The immune response to sexually transmitted chlamydial infections in animals will be studied using the gp-ic model.